The transcription factor E2F1 induces both proliferation and apoptosis and is a critical downstream target of the tumor suppressor RB.Long non-coding RNAs (lncRNAs) are major regulators of many cellular processes, including cell cycle progression and cell proliferation. However, the mode of action as well as the transcriptional regulation of most lncRNAs are only beginning to be understood.Here, we report that a novel human lncRNA, LAPAS1, is an E2F1-regulated lncRNA that affects S phase progression. Inhibition of LAPAS1 expression increases percentage of S phase cells, and its silencing in synchronized cells delays their progression through S phase. In agreement with its suggested role in cell cycle progression, prolonged inhibition of LAPAS1 attenuates proliferation of human cancer cells.Our data demonstrate that LAPAS1 predominantly functions in trans to repress expression of Sphingolipid Transporter 2 (SPNS2). Importantly, knockdown of SPNS2 rescues the effect of LAPAS1 silencing on cell cycle and cell proliferation.Notably, low levels of LAPAS1 are associated with increased survival of kidney cancer patients.Summarily, we identify LAPAS1 as a novel E2F-regulated lncRNA that has a potential role in human cancer and regulates cell-cycle progression and cell proliferation, at least in part, via regulation of SPNS2.

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Long non-coding RNAs (lncRNAs) are major regulators of many cellular processes including cell cycle progression and cell proliferation. The pivotal transcription factor E2F1 induces both proliferation and cell death and is a critical downstream target of the tumor suppressor RB. The RB/E2F pathway is often inactivated in human tumors resulting in deregulated E2F activity. Here, we report that the human lncRNA XLOC_000190 is an E2F1- regulated lncRNA that plays a role in S phase progression. XLOC_000190 levels are elevated upon activation of E2F1. Furthermore, knockdown of E2F1 and E2F3 reduce XLOC_000190 levels and endogenous E2F1 binds the XLOC_000190 promoter. Moreover, expression of XLOC_000190 is cell cycle regulated and peaks near G1/S transition and in early S. Inhibition of XLOC_000190 expression increases percentage of S phase cells, suggesting that XLOC_000190 plays a role in S phase progression. Also, silencing of XLOC_000190 in cells that are synchronized at the G1/S delays progression of cells through S phase. In agreement with its suggested role in S phase, prolonged silencing of XLOC_000190 inhibits proliferation of human cancer cells in culture. XLOC_000190 is a nuclear lncRNA and its gene is localized downstream to the protein-coding gene CDKN2C that encodes the p18ink4c CDK inhibitor. In search for XLOC_000190 mode of action we do not detect any changes in the expression of this neighbor upon XLOC_000190 silencing. However, XLOC_000190 silencing leads to a significant decrease in the level of Ribonucleotide Reductase Regulatory Subunit M2 (RRM2), which is a critical player in S phase progression. Additional data indicate that RRM2 mediates, at least in part, the effect of XLOC_000190 on S phase progression. Importantly, low levels of XLOC_000190 are associated with increased survival of kidney cancer patients. In conclusions, our data identify XLOC_000190 as a novel E2F-regulated lncRNA that has a potential role in human cancer and regulates cell-cycle progression and cell proliferation, at least in part, via regulation of RRM2. Citation Format: Doron Ginsberg, Tali Nizri-Megnaji, Esther Baruch. A novel E2F1-regulated lncRNA, XLOC_000190, is required for S phase progression and cell proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3567.